Standard cognition test falls short in Parkinson’s disease patients

By Eleanor McDermid, Senior medwireNews Reporter

There is a wide range of cognitive function, including dementia, among patients with Parkinson’s disease (PD) who are classed as cognitively normal on the Mini-Mental State Examination (MMSE), research shows.

“If the MMSE were used as the only instrument to detect dementia in PD, as is the case in many clinical settings, 55% of the dementia cases in our study would have been missed”, the study authors observe in Movement Disorders.

James Leverenz (Cleveland Clinic Foundation, Ohio, USA) and co-workers studied 788 PD patients who were classified as cognitively normal, based on a MMSE score of at least 26.

However, the results of individual neuropsychological assessments gave a different picture, with more than 20% of patients scoring at least 1.5 standard deviations (SDs) below normal in eight of the 15 tests used.

For example, 31.1% scored at least 1.5 SDs below normal in the Digit Symbol Coding test, as did 28.6% for delayed recall in the revised Hopkins Verbal Learning Test. In all, 67% of the patients scored at least 1.5 SDs below normal on at least one test.

A total of 342 patients at a single centre received a clinical consensus cognitive diagnosis, 290 of whom had MMSE scores of at least 26. Based on the in-depth neuropsychological cognitive test results, 58.6% received a consensus diagnosis of mild cognitive impairment and 15.0% of dementia. This gave the MMSE a sensitivity for dementia of just 45% and a specificity of 94%.

Patients rated as normal on the MMSE also had a broad range of cognitive abilities on the Montreal Cognitive Assessment (MoCA), with 51.9% being classed as impaired. However, the researchers stress that the MoCA also has “important limitations”, including reduced specificity, which are to be expected in a tool developed, like the MMSE, for use as a screening measure.

“Given these results and those of previous studies, clinicians should be cautious when using the MMSE as a bedside test to detect [cognitive impairment] in PD, and should consider referring patients with cognitive concerns for more detailed neuropsychological assessments”, concludes the team.

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